This invention relates to a device for omnidirectionally measuring the intensity of a vertical electromagnetic field independently of frequency in a given range, using an antenna to sense the incident field.
Modern ordnance systems often employ sensitive, electrically-initiated explosive elements, known as electroexplosive devices (EED's) to activate control and arming devices and to initiate explosive trains. The proliferation of EED's has raised the concern of their accidental detonation by powerful radar and communications equipment. The frequency range of greatest concern is 2MHz to 32MHz, since it is in this range that the smallest electromagnetic field intensity can cause accidental EED detonation.
Consequently, it is of great importance to be able to measure, in the 2MHz to 32MHz range, small (less than 0.2 volts/meter) vertical electric field intensities in which the measurement is omnidirectional, independent of frequency, and in standard vertical electromagnetic field intensity units of general application. Any field intensity indicating device for the protection of EED's must also be able to sum the total resultant field when several electromagnetic sources are radiating from a variety of directions in the vicinity of the EED. Additionally, such a meter should be compact, simple, not subject to drift, nor sensitive to the presence of personnel.
None of the electromagnetic-field intensity measuring devices heretofore known have had this capability. The previously used method of measuring electromagnetic field intensity in the 2MHz to 32MHz range used a tunable narrow-bandwith device. If several sources were radiating, a separate measurement for each frequency transmitted would be required, and then each of the readings at each frequency had to be converted to field strength, and then the square root of the sum of the squares would have to be taken to complete the total vertical electromagnetic field strength measurement. This meter was also bulky, complicated and subject to drift and to the presence of personnel.
Another device, described in U.S. Pat. No. 3,063,010, uses a symmetrical antenna to monitor the thermogenic action of R.F. energy and its potential effects on the human body. This device does not measure electromagnetic field intensity in standard vertical electric field intensity units, however, and thus would be useless to warn against the potential hazards of electromagnetic field strength to EED's.
Another device is described in U.S. Pat. No. 3,130,368 which uses a spiral antenna to monitor electromagnetic radiation omnidirectionally and independently of frequency within a fixed frequency range. The frequency range in which this device operates is from 200MHz to 10GHz. This frequency range is far above the 2MHz to 32MHz range in which the greatest hazards to accidental EED detonation occur. The device of this patent would be ineffective as a warning device against accidental EED detonation in this lower frequency range.